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HA coating generally unnecessary in primary total hip replacement
Survival rate without HA-coated stems is 97.7%; coating may be required for revision.
ORLANDO, U.S.A. – A recent Austrian study suggests that a hydroxyapatite coating is only useful for total hip replacement in extreme situations such as massive osteoporosis or revision surgery.
In 4253 primary hip replacement surgeries performed from 1992 to 2005 at the Orthopaedic Hospital Gersthof, only four cemented stems and 65 (1.5%) hydroxyapatite (HA)-coated stems were used, as Karl Zweymüller, MD, director of the Orthopaedic Hospital Gersthof, Vienna, said at the 22nd Annual Current Concepts in Joint Replacement Winter 2005 Meeting.
At 10-year follow-up, 215 consecutive patients without an HA coating had a 97.7% survival rate. Two stems showed radiologic loosening.
“This rate lies at the top outcome category of the Swedish Hip Arthroplasty Register and suggests that an HA coating is unnecessary,” Zweymüller said.
Excellent results
Nine surgeons performed total hip arthroplasty on the 215 patients (mean age 62.6 years), using the SL-Plus stem (Plus Orthopaedics AG) from January 1993 to May 1994. At the mean 10.2-year follow-up, researchers found six revisions: two aseptic loosenings, one low-grade infection, two periprosthetic fractures and one traumatic subsidence. Stem position was unchanged at follow-up.
Courtesy of Felix Lintner |
The Kaplan-Meier survivorship curve showed a 97.7% survivor rate, including the six revisions. “Our findings indicate that in osseointegrated titanium stems, one can expect good long-term results,” Zweymüller said.
Released in 1993, the SL-Plus stem has a surface roughness of 3 µm to 5 µm and a taper also in the sagittal dimension. Zweymüller explained that the osteoconductive material and the rough surface of the SL-Plus stem stimulate new bone formation and ensure excellent secondary stability by osseointegration. Integration was already seen on histology 10 days after surgery.
A 79-year-old female cadaver specimen showed new bone formation – especially in the edge region – at 2.5 months postop. An 83-year-old woman had similar findings at 20.7 years after surgery with pronounced osseous fixation of the edge regions of the implant. Despite severe osteoporosis, there was “an absolutely stable situation,” Zweymüller said.
He found that osteoporosis and age are not contraindications for primary total hip replacement without an HA coating.
“Osteoporosis, for me, is no contraindication … because if you do proper reaming without changing position of the instrument, and if you find the exact same way for tapping the definitive stem, there is no danger at all,” he said.
At the time of histologic examination, the researchers found no difference in bone-to-implant contact areas between patients younger than 65 years and those older than 65 years at the time of surgery. At retrieval, patients aged 80 years or older showed the same rates as younger patients. Researchers discovered that medullary canal widening does not affect stability in the following decades.
HA necessary for revision
Zweymüller reported that an osteoinductive surface with HA is useful in special instances only. For example, 19 years after surgery, a female patient experienced loosening due to wear with an old cementless poly cup. Surgeons used a HA-coated stem for her revision and five years later, the gaps found prior to revision were filled up spontaneously by newly formed bone.
In another 83-year-old female, new bone formed directly toward the implant surface three months after revision with a HA-coated stem, despite severe osteoporosis.
According to Zweymüller, the fixation principle has not changed since 1979 when the first-generation cementless, straight, tapered stems were introduced. The second generation was released in 1986 and showed a more uniform pattern of bone coverage in histology compared to the first-generation stems.
“This system works … because of the rectangular cross-section, the tapered straight stem, metadiaphyseal anchorage and pressfit fixation, thus achieving primary stability,” Zweymüller said.
Dr. Zweymüller has a financial interest in a product mentioned in this article.
For more information:
- Zweymüller K. No coating required: a pressfit alternative. #12. Presented at the 22nd Annual Current Concepts in Joint Replacement Winter 2005 Meeting. Dec. 14-17, 2005. Orlando, U.S.A.